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<p>In order to probe the impact that salts containing weakly coordinating anions might have on electrophilic transformations of industrial significance (e.g., Friedel-Crafts alkylation, nitration) initial studies were conducted on the aqueous cationic polymerization of an easy to handle monomer (styrene). It was hypothesized that the addition of minute quantities of a salt bearing a weakly coordinating anion may enhance the activity of traditional acid catalysts that are employed to effect such reactions. This article details preliminary results for the polymerization of a solution of this olefin, in toluene or dichloromethane, containing a small quantity of a carborane salt (i.e., Cs<sup>+</sup>[CHB<sub>11</sub>Cl<sub>11</sub>]<sup>−</sup>) as a catalyst, suspended in a continuous phase of HCl(aq). In the absence of this salt no conversion of neat styrene is obtained even when reaction is conducted in fuming hydrochloric acid at room temperature for a period of one week, whereas explosive polymerization ensues in its presence almost instantly. Likewise, the olefin is stable in the presence of the salt provided that HCl(aq) is absent. This approach is believed to generate small quantities of a hydrophobic superacid (i.e., H<sup>+</sup>[CHB<sub>11</sub>Cl<sub>11</sub>]<sup>−</sup>) via a metathetical reaction between the Brønsted acid component of the aqueous phase and the catalytic salt contained in the organic phase where the resultant strong acid then initiates polymerization of the olefin. Addition of a common salt (i.e., CsCl) was found to reduce conversion and argues in favor of the in situ generation of a superacid within the monomer droplet. These reactions produce polymers with molecular weights showing expected dependencies on solvent polarity, chain end functionalities, and Arrhenius plots of <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\overline {{\text{M}}} _{\text{w}}}\)</EquationSource> </InlineEquation>, that are consistent with a cationic mechanism. In the presence of toluene polymerization was found to have two stages, a fast initial reaction followed by a slower second phase. The latter stage was determined to be first order with respect to the monomer. Since the strong acid is continuously regenerated in situ these polymerizations are catalytic and indefinitely active in nature.</p> Graphical Abstract <p></p>

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In-Situ Generation of Superacids for Aqueous Catalytic Cationic Polymerization: Preliminary Results for the Polymerization of Toluene and Dichloromethane Solutions of Styrene/Cs+[CHB11Cl11]− Suspended in HCl(aq)

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Stewart P. Lewis

摘要

In order to probe the impact that salts containing weakly coordinating anions might have on electrophilic transformations of industrial significance (e.g., Friedel-Crafts alkylation, nitration) initial studies were conducted on the aqueous cationic polymerization of an easy to handle monomer (styrene). It was hypothesized that the addition of minute quantities of a salt bearing a weakly coordinating anion may enhance the activity of traditional acid catalysts that are employed to effect such reactions. This article details preliminary results for the polymerization of a solution of this olefin, in toluene or dichloromethane, containing a small quantity of a carborane salt (i.e., Cs+[CHB11Cl11]−) as a catalyst, suspended in a continuous phase of HCl(aq). In the absence of this salt no conversion of neat styrene is obtained even when reaction is conducted in fuming hydrochloric acid at room temperature for a period of one week, whereas explosive polymerization ensues in its presence almost instantly. Likewise, the olefin is stable in the presence of the salt provided that HCl(aq) is absent. This approach is believed to generate small quantities of a hydrophobic superacid (i.e., H+[CHB11Cl11]−) via a metathetical reaction between the Brønsted acid component of the aqueous phase and the catalytic salt contained in the organic phase where the resultant strong acid then initiates polymerization of the olefin. Addition of a common salt (i.e., CsCl) was found to reduce conversion and argues in favor of the in situ generation of a superacid within the monomer droplet. These reactions produce polymers with molecular weights showing expected dependencies on solvent polarity, chain end functionalities, and Arrhenius plots of \({\overline {{\text{M}}} _{\text{w}}}\) , that are consistent with a cationic mechanism. In the presence of toluene polymerization was found to have two stages, a fast initial reaction followed by a slower second phase. The latter stage was determined to be first order with respect to the monomer. Since the strong acid is continuously regenerated in situ these polymerizations are catalytic and indefinitely active in nature.

Graphical Abstract